A conventional pneumatic tool has a pneumatic turbine motor driven by compressed air to generate rotation. The pneumatic turbine rotates to generate a centrifugal force which incorporates with a flexible O-ring to control the size of an air inlet and an outlet to stabilize rotation speed of the pneumatic turbine motor.
For instance U.S. Pat. No. 7,077,732 discloses a dual chamber turbine rotor which has a turbine including a spacer and a front cap and a rear cap at two ends to form a first chamber and a second chamber. The front cap and rear cap and two sides of the spacer have respectively a corresponding trough to hold a barrier. The first and second chambers hold respectively an O-ring and have an air passage leading to an air outlet located on an outer side of the turbine. When compressed air enters the pneumatic turbine motor, it presses the O-ring against the barrier such that the compressed air passes through the barrier and air passage to be discharged through the air outlet. Thereby the pneumatic turbine rotor is driven and rotates. The dual chamber design can boost air displacement of the compressed air. Thus the torque of the pneumatic turbine rotor is boosted without increasing the size and weight of the total pneumatic turbine rotor.
However, as the barrier is located separately in the turbine, when in use it is deformed or dislocated due to pressing of the O-ring caused by the compressed air, or even broken. As a result, the torque generated by the pneumatic turbine rotor is uneven.